Pathogen-induced systemic activation of a plant defensin gene in Arabidopsis follows a salicylic acid-independent pathway.

A 5-kD plant defensin was purified from Arabidopsis leaves challenged with the fungus Alternaria brassicicola and shown to possess antifungal properties in vitro. The corresponding plant defensin gene was induced after treatment of leaves with methyl jasmonate or ethylene but not with salicylic acid or 2,6-dichloroisonicotinic acid. When challenged with A. brassicicola, the levels of the plant defensin protein and mRNA rose both in inoculated leaves and in nontreated leaves of inoculated plants (systemic leaves). These events coincided with an increase in the endogenous jasmonic acid content of both types of leaves. Systemic pathogen-induced expression of the plant defensin gene was unaffected in Arabidopsis transformants (nahG) or mutants (npr1 and cpr1) affected in the salicylic acid response but was strongly reduced in the Arabidopsis mutants eln2 and col1 that are blocked in their response to ethylene and methyl jasmonate, respectively. Our results indicate that systemic pathogen-induced expression of the plant defensin gene in Arabidopsis is independent of salicylic acid but requires components of the ethylene and jasmonic acid response.     

Phenylalanine ammonia-lyase in potato (Solanum tuberosum L.). Genomic complexity, structural comparison of two selected genes and modes of expression.

Potato (Solanum tuberosum L. cv. Datura) contains approximately 40-50 phenylalanine ammonia-lyase (PAL) genes/haploid genome. Considerable cDNA heterogeneity indicates that at least about 10, and probably more, of these genes are potentially active. One subfamily, represented by one selected member (PAL-1), was analyzed with respect to genomic complexity, nucleotide and deduced amino acid sequence, and mode of constitutive or induced expression. For comparison, a second gene (PAL-2), representing several subfamilies that are easily distinguished from PAL-1, was included in these studies. Extensive structural similarities were observed both between the TATA-proximal portions of the PAL-1 and PAL-2 promoters, particularly in the areas containing putative cis-acting elements, and among all presently known PAL proteins from various higher and lower plants. The relative abundance of PAL mRNA varied greatly in several major potato organs. However, the patterns obtained with probes detecting either total PAL mRNA or more specifically, PAL-1-related or PAL-2-related mRNA species, were the same within experimental error. Mature leaves contained particularly low levels of PAL mRNA. Infection of these leaves with the pathogenic fungus, Phytophthora infestans, resulted in a large, transient induction of PAL mRNA. The relative timing of PAL-1 and PAL-2 mRNA expression, however, differed in compatible (fungus virulent, plant susceptible) but not in incompatible interactions (fungus avirulent, plant resistant). Wounding of leaves caused an extremely rapid and transient induction of both PAL mRNA species.     

A gene encoding a chloroplast-targeted lipoxygenase in tomato leaves is transiently induced by wounding, systemin, and methyl jasmonate.

We investigated the relationship between the expression of lipoxygenase (LOX) genes and the systemin-dependent wound response in tomato (Lycopersicon esculentum) leaves. A polymerase chain reaction-based approach was used to isolate two tomato Lox cDNAs, called TomLoxC and TomLoxD. Both TomLOXC and TomLOXD amino acid sequences possess an N-terminal extension of about 60 residues that were shown by in vitro uptake to function as transit peptides, targeting these proteins into the chloroplast. Within 30 to 50 min following wounding or systemin or methyl jasmonate treatments, the TomLoxD mRNA level increased and reached a maximum between 1 and 2 h. TomLoxC mRNA was not detectable in leaves and was not found following wounding, but it was found in ripening fruits, indicating that the two tomato Lox genes are regulated in different tissues by different processes. The results suggest that the TomLoxD gene is up-regulated in leaves in response to wounding and encodes a chloroplast LOX that may play a role as a component of the octadecanoid defense-signaling pathway.     

Molecular characterization of a novel lipase-like pathogen-inducible gene family of Arabidopsis

In a differential screening between Arabidopsis plants pretreated with the resistance-inducer beta-aminobutyric acid and untreated control plants, we have identified a gene encoding a novel lipase-like protein, PRLIP1. The abundance of PRLIP1 mRNAs in Arabidopsis leaves was up-regulated by application of beta-aminobutyric acid, salicylic acid (SA), and ethylene as well as by various pathogens. Induction of PRLIP1 depended on a functioning SA and ethylene signal transduction pathway but was independent of jasmonate signaling. This novel pathogenesis-related (PR) gene of Arabidopsis belongs to a gene family consisting of six (PRLIP1, PRLIP2, PRLIP4, PRLIP5, PRLIP6, and PRLIP7) closely related members in tandem position on chromosome 5. Among these genes, PRLIP2 also was induced in leaves by SA and infections by pathogens but on a much lower level than PRLIP1. The PRLIP1 family showed a tissue-specific expression pattern. Both PRLIP1 and PRLIP2 were specifically expressed in leaves and siliques, PRLIP1 additionally in stems and flowers. The expression of PRLIP6 and PRLIP4 was root specific, whereas mRNA of PRLIP5 and PRLIP7 were not detected in any of these tissues. The more distantly related genes PRLIP3, PRLIP9, and PRLIP8 were found on chromosomes 2, 4, and 5, respectively. The expression level of PRLIP3 was checked and found constitutive during the different stress conditions tested. The PRLIP1 gene was overexpressed in Escherichia coli, and the resulting PRLIP1 protein showed esterase activity on p-nitrophenyl-butyrate and allowed the growth of the bacteria on lipidic substrates such as Tween20 or Tween80.     

水稻OsFAD2、OsFAD6的克隆及其家族成员对非生物胁迫的响应

植物中的不饱和脂肪酸由脂肪酸去饱和酶(Fatty acid desaturase, FAD)合成, 它在植物的生长发育以及植物非生物胁迫方面起着重要的作用。文章采用RT-PCR方法, 从水稻日本晴(Oryza sativa L.)中克隆了分别与FAD2、FAD6同源的脂肪酸脱氢酶序列, 命名为OsFAD2和OsFAD6。OsFAD2的ORF为1 167 bp, 推测其编码蛋白含有388个氨基酸, 等电点为8.17, 分子量为52.24 kDa, C端有内质网定位序列; OsFAD6的ORF长度为1 365 bp, 推测编码454个氨基酸的蛋白质序列, 分子量44.35 kDa, 等电点为9.24, 推测N端38个氨基酸为叶绿体导肽。两者都具有膜整合脂肪酸去饱和酶特有的3个组氨酸簇。RT-PCR分析表明, OsFAD2和OsFAD6在水稻所有器官中都表达, 在叶中表达量为最高。在水稻FAD基因家族中, 叶中OsFAD2、OsFAD6 的mRNA对低温不响应, 而OsFAD7和OsFAD8的 mRNA在低温下上升。水稻叶中OsFAD2、OsFAD6、OsFAD3和OsFAD7的mRNA表达具有昼夜节律性, 在光照下表达量低, 而在随后的黑暗中表达量高, OsFAD6和OsFAD7 mRNA表达的昼夜节律性可能与水稻幼苗叶片中NADPH量的改变有关。     

Two tomato non-symbiotic haemoglobin genes are differentially expressed in response to diverse changes in mineral nutrient status

The role of plant non‐symbiotic haemoglobins remains undefined, but recent findings suggest a possible role in plant nitrate nutrition. This study sought to characterize patterns of gene expression for two tomato (Lycopersicon esculentum L.) non‐symbiotic haemoglobin genes, and to examine how diverse changes in nutrient status influences the expression of these two genes. The deduced amino acid sequences of the genes examined, SOLly GLB1 and SOLly GLB2, are 55% identical. SOLly GLB1 mRNA is present in highest abundance in roots and older stems, whereas SOLly GLB2 mRNA abundance is highest in leaves, but detectable in other tissues including roots. The SOLly GLB1 mRNA levels increased rapidly in roots in response to each nutrient treatment examined in hydroponic culture, including the individual removal of phosphate, potassium and iron from the culture medium, as well as by the addition of nitrate. In contrast, the levels of SOLly GLB2 mRNA were not significantly altered in response to these same treatments. These results are the first report that non‐symbiotic haemoglobin gene expression can be influenced by a broad range of changes both in mineral macronutrient and micronutrient status, suggesting a previously unrecognized generic role for non‐symbiotic haemoglobins in processes associated with mineral nutrient nutrition.     

Characterization of an Arabidopsis lipoxygenase gene responsive to methyl jasmonate and wounding.

A cDNA corresponding to the gene AtLox2 was isolated from an Arabidopsis thaliana library using a lipoxygenase (LOX) probe from soybean. AtLox2 encodes a 102-kD protein, AtLOX2, which has 42 to 45% amino acid sequence identity with other plant LOX sequences. The AtLOX2 sequence is more than 30 amino acids longer at the amino terminus than other plant LOX sequences, and this extension has features reminiscent of chloroplast transit peptides, suggesting that AtLOX2 may be chloroplast localized. AtLox2 mRNA levels are high in leaves and inflorescences but very low in seeds, roots, and stems. AtLox2 mRNA accumulation is rapidly induced in leaves in response to methyl jasmonate. Leaves that have been wounded and adjacent leaves on the same plant also accumulate AtLox2 mRNA.